Control systems for engines

ABSTRACT

A control system, particularly for a compression-ignition engine, has an actuator for controlling the setting of a part associated with the engine, and an oscillator from which is derived an a.c. signal having an amplitude dependent on the value of a system parameter. This signal is fed to a capacitor by way of a switching device, and the capacitor provides an input to the control circuit. Means is provided operating in synchronism with the oscillator for controlling the switching device so that it conducts only when the a.c. signal has stabilised.

United States Patent Williams et al.

[451 Jan. 21, 1975 CONTROL SYSTEMS FOR ENGINES Inventors: Malcolm Williams, Solihull;

Geoffrey Albert Kenyon Brunt, Glastonbury; Christopher Robin Jones, Alcester, all of England Assignee: C. A. V. Ltd., Birmingham, England Filed: Apr. 4, 1973 Appl. N0.: 347,701

Foreign Application Priority Data Apr. 4, 1972 Great Britain 15366/72 US. Cl 123/32 EA, 123/139 E, 60/3928, 308/158, 307/247, 73/398 Int. Cl F02b 3/00, G011 9/00, Fl6c 17/06 Field of Search 60/3928; 123/102, 139 E, 123/32 AH, 32 EA; 308/165, 158; 307/247, 266, 268; 73/398 References Cited UNITED STATES PATENTS 6/1972 Konno 1/268 3,673,989 7/1972 Aono 123/32 EA 3,718,123 2/1973 Eckert l/l 3,725,675 3/1973 Olsen 307/247 R Primary Examiner-Charles .l. Myhre Assistant Examiner-Ronald B. Cox Attorney, Agent, or Firm-H0lman & Stern [57] ABSTRACT A control system, particularly for a compressionignition engine, has an actuator for controlling the setting of a part associated with the engine, and an oscillator from which is derived an ac. signal having an amplitude dependent on the value of a system parameter. This signal is fed to a capacitor by way of a switching device, and the capacitor provides an input to the control circuit. Means is provided operating in synchronism with the oscillator for controlling the switching device so that it conducts only when the ac. signal has stabilised.

12 Claims, 7 Drawing Figures ACTUATOR\ SPEED TRANSDUCER AMPLIFIER CONTROL CIRCUIT MONOSTABLE CIRCUITS CIRCUIT DEMAND TRANSDUCER 80 Patented Jan. 21, 1975 I 3,861,363

2 Sheets-Shut 1 ACT'UATO. /|7 II I2 l3 R E fiz wgoucaa I I I I PUII/IP ENCIINE AMPLIFIER I CONTROL l l I I I v 25 MECHANICAL 27 36 8 SWITEH' I 22 //OSCILLATOR 26 26 I 51 limb I} IO I L4 v 2|.

I 32 5| MONOSTABLE CIRCUITS MECHANICAL LINE OSCILLATOR MONOSTABLE CIRCUITS FIGZ.

Patented Jan. 21, 1975 3,861,363

2 Sheath-Shut 2 PUMP I7 125 n ENGINE l2 ACTUA OR\\ 4 TRPAEVAQQED 'Z/ s EED CONTROL; I TRANSDUCER I6 15 0 AMPLIFIER :13 /5 l ggER i-bg 47 1/ 43/ 9 CURRE 6 |Q gouge?) M i m RG6.

SPEED PUMP OUTPUT SPEED F- CONTROL SYSTEMS FOR ENGINES This invention relates to control systems for engines.

In one aspect, the invention resides in a system comprising in combination an actuator for controlling the setting of a part associated with the engine, a control circuit coupled to the actuator to determine the position of said part, an oscillator, means deriving from said oscillator an a.c. signal having an amplitude dependent on the value of a system parameter, a switching device by way of which said a.c. signal is fed to a capacitor, the voltage across the capacitor providing an input to the control circuit, and means operable in synchronism with the oscillator for turning the switching device on at periods during the operation of the oscillator when said a.c. signal has stabilised.

In another aspect, a system according to the invention comprises in combination an actuator for controlling the setting of a part associated with the engine, a control circuit coupled to the actuator to determine the position of said part, a transformer having a primary winding and a secondary winding, the primary winding being coupled to an oscillator and the secondary winding being connected through a switching device to a capacitor, means responsive to a system parameter for varying the coupling between the primary and secondary windings of the transformer and means operable in synchronism with the oscillator for turning the switching device on at periods during the operation of the oscillator when the voltage across the secondary winding has stabilised, whereby the voltage across the capacitor is indicative of the setting of the means for varying the coupling, the voltage across the capacitor providing an input to the control circuit.

In a third aspect, the invention resides in a fuel supply system for an engine, comprising in combination a pump for supplying fuel to the engine, pump control means for determining the output of the pump, a first transducer for producing a first electrical signal representing pump output, a second transducer for producing a second electrical signal representing demand, means for producing a third electrical signal representing engine speed, a control circuit to which the first, second and third electrical signals are applied, the control circuit operating the pump control means to give the required pump output, at least one of said transducers comprising a transformer having its primary winding connected to an oscillator, and arranged so that the coupling between the primary and secondary windings is determined by the value of the parameter sensed by the transducer, whereby the amplitude of the a.c. signal in the secondary winding of the transformer is determined by the value of said parameter, a capacitor, a switching device coupling the secondary winding to the capacitor, and means operable in synchronism with the oscillator for turning the switching device on at periods during the operation of the oscillator when the voltage across the secondary winding has stabilised, whereby the voltage across the capacitor is indicative of the value of said parameter, the voltage across the capacitor providing an input to the control circuit.

In the accompanying drawings,

FIG. 1 is a circuit diagram, partly in block form, illustrating one example of the invention as applied to a fuel system for a compression-ignition engine.

FIG. 2 illustrates a modification of the example shown in FIG. 1,

FIG. 3 illustrates one form of control circuit for use in FIG. 1,

FIGS. 4 to 6 illustrate the outputs of three transducers used in FIG. 3, and

FIG. 7 illustrates the operating characteristics of an engine controlled by the arrangement in FIGS. 3 to 6.

Referring to FIG. 1, an engine part in the form of a pump 11 supplies fuel to the engine 12, the speed of which is sensed by a transducer 13 providing one input to a control circuit 14. The control circuit 14 also receives an input from a transducer 20 sensing demanded engine speed, and produces an output to a power amplifier 16, the output from which controls an electromechanical actuator 17 operating a control rod 18 forming part of the pump 11 and controlling the output of the pump 11. The control rod is spring loaded toward the minimum fuel position and may be operated directly by the actuator or indirectly by an hydraulic servo in which case the actuator operates a valve. The control circuit 14 receives a third signal, in a manner to be described, from a current amplifier 15, this signal representing the actual position of the control rod 18 at any given moment. The circuit 14 compares the signals it receives and increases or reduces the fuel supply in accordance with the values of the signals. The signal representing the position of the control rod 18 provides the required fuel-speed demand characteristics.

In order to provide the signal representing the position of the control rod, there is provided a square wave oscillator 21 which'is connected across positive and negative supply lines 8, 9 and the output of which is connected to the primary winding 22 of a variable coupling transformer having a secondary winding 23, and a core part which is movable and is indicated at 24. The arrangement is such that the position of the part 24 determines the amplitude of the signal in the winding 23. Any convenient means 25 is provided for moving the part 24, the means 25 being itself sensitive to the position of the control rod 18. In its simplest form, the means 25 can just be a link, and it will be appreciated that with this arrangement the amplitude of the signal in the winding 23 will be a representation of the position of the control rod 18, and therefore the rate of supply of fuel to the engine.

The winding 23 has one end connected to a line 10 maintained at a potential mid-way between the potential of the lines 8, 9 and is bridged by resistors 36, 26 in series, the resistor 26 being bridged by a switching device 27 and a capacitor 28 in series, and the junction of the device 27 and capacitor 28 being connected through the amplifier 15 to the control circuit 14, so that the control circuit 14 receives a signal representing the voltage across the capacitor 28. In a practical situation the device 27 and the capacitor 28 are connected to the transformer by way of a cable of substantial length, as indicated by the dotted lines in FIG. 1.

Since the oscillator 21 is a square wave oscillator, the output from the winding 23 will be of substantially square wave form, but at the commencement of each square wave, owing to the self capacitance of the cable the circuit will resonate and so the amplitude will not be strictly proportional to the control rod position. Oscillations produced during this period are damped by the resistor 36, 26, and the switching device 27 only turns on after the oscillations have been sensibly damped, so that the voltage across the capacitor 28 is an accurate representation of the control rod position.

This is accomplished by virtue of two monostable circuits 31 and 32. The monostable circuit 31 receives an input from the oscillator 21 at the commencement of a square wave, and remains in its unstable state for a period during which the resistors 36, 26 damps the oscillation. At the end of this period, the monostable circuit 31 reverts to its stable state, and in so doing drives the monostable circuit 32 to its unstable state. When the monostable circuit 32 is in its unstable state, it turns on the switching device 27, which conveniently is a field effect or other transistor, and after a period of time when the monostable circuit 32 reverts to its stable state, the switching device is turned off. It will be appreciated that in this way the switching device 27 not only rectifies the output signal from the winding 23, but also ensures that sampling of the signal from the output winding 23 only occurs when the oscillations in the signal have died down. In this manner the cable length becomes less important.

Since the resistors 26, 36 serve the same function, one of them can be omitted in some applications.

Referring now to the example shown in FIG. 2, the arrangement is similar to that shown in FIG. 1 except that a capacitive transducer is employed. Thus, the oscillator 21 has connected across it a pair of capacitors 33, 34 in series, with the junction of the capacitors 33, 34 is connected through a resistor 30 to the switching device 27. The means 25 varies the value of the capacitor 33, and the operation is exactly the same as in FIG. 1. The problem is also the same as in FIG. 1, except that the cause of the problem is now lead inductance in combination with the capacitors 33 and 34. As will be appreciated, the problem is solved in the same way as in FIG. 1.

FIG. 3 shows one form of the control circuit 14 seen in FIG. 1. The control circuit includes a pair of operational amplifiers 41, 42 having their output terminals connected through diodes 43, 44 respectively to the amplifier 16. Each of the amplifiers 41, 42 is connected between the lines 8, 9 and the non-inverting inputs of the amplifiers 41, 42 are connected to the line 10. The amplifiers are connected to act as summing amplifiers, and for this purpose resistors 45, 46 are connected between the input of the amplifier 16 and the inverting inputs of the amplifiers 41, 42. The purpose of coupling the feedback resistors 45, 46 to the input of the amplifier 16 is so that the temperature characteristics of the diodes 43, 44 do not substantially affect the operation of the circuit.

The transducer 13 produces a voltage output of the form shown in FIG. 4, and is coupled to the inverting input of the amplifier 41 through a resistor 47. The transducer 20 produces an output voltage of the form shown in FIG. 6, and this output is coupled to the inverting input of the amplifier 41 through a resistor 48. The output from the amplifier is a voltage of the form shown in FIG. 5, and this output is coupled through resistors 49, 51 to the inverting inputs to the amplifiers 41, 42 respectively. The origin in FIGS. 4 to 6 is the potential of the terminal 10. There are also provided two current sources 52, 53 coupled to the inverting inputs of the amplifiers 41, 42 respectively for a purpose to be explained, and a control 54 which is coupled to the transducer 20.

The operation of the arrangement shown in FIG. 3 is best explained with reference to FIG. 7. Ignoring for the moment the amplifier 42, the amplifier 41 compares the current flowing through the resistors 49 and 47 with the current flowing through the resistor 48, and produces an output to the amplifier 16 which modifies the fuel flow to give the required engine characteristics. The line 61 in FIG. 7 is one of a family of lines representing demanded engine speed. Thus, if the pedal is set in a position such that the demand is indicated by the line 61, then the engine will operate at a point on the line 61 determined by the load on the engine.

The purpose of the amplifier 42 is to restrict the maximum pump output to a predetermined value, indicated in FIG. 7 by the line 63. When the amplifier 41 is producing an output to operate the amplifier 16, the diode 44 is reverse biased. However, as the amplifier 41 demands more fuel, its output decreases, because the circuit is so arranged that smaller output from the amplifier 41 represents a demand for more fuel. When the output from the amplifier 41 falls to a value such that it is smaller than the output from the amplifier 42, then the diode 44 starts to conduct, and reverse biases the diode 43. The amplifier 42 now controls the amplifier l6, and the maximum pump output is restricted to the line 63 shown in FIG. 7, this line being set by the source 53.

The boundary line 65 shown dotted in FIG. 7 is a function of the engine, not the governor, and represents the no-load fuel requirements of the engine under different demands.

It will be appreciated that FIG. 7 explains how the engine will behave in any circumstances. Suppose that the pedal has been set to a demand represented by the line 61. As previously explained, the exact position on the line 61 at any given instant will depend on the load on the engine. Thus, if the vehicle starts to go up an incline, the load will increase, and if the pedal is not moved, the operating point will move up the line 61. If the load becomes sufficiently greater, the line 63 is reached, and no further increase in pump output is permitted. At this point the speed falls rapidly. If the load decreases, then the operating point moves down the line 61 with corresponding increase in speed. If the load decreases to zero, the line 65 is reached.

If the demand is changed, then assuming for convenience that maximum demand is called for, the pump output will increase as rapidly as the pump and governor will allow until the line 63 is reached, and the engine will then move along the lines 63, 64 to a point on the line 64 determined by load. If the demand is reduced, for example to zero, then the pump output will decrease as rapidly as the pump and governor will allow until the fuel supply is zero. The speed then decreases until the line 62 is reached, and the operating point settles on the line 62 at a position determined by load.

It will of course be appreciated that the control circuit can take a variety of forms. In another example, the transducer 20 demands a particular fuel, rather than a particular speed. In such an arrangement, the line 61 extends horizontally in FIG. 7. The circuit of FIG. 3 can be employed in such an arrangement with suitable modifications. Thus, the transducer 13 now provides an input to the amplifier 42, but not to the amplifier 41. The input to the amplifier 42 from the transducer 13 enables the amplifier 42 to set the line 64. It will be appreciated that the slope on the line 64 is obtained by virtue of the input to the amplifier 42 by way of the resistor 51. The amplifier 41 now compares demanded fuel with actual fuel and produces the required horizontal line replacing the line 61 in FIG. 7. The control 54 now limits the maximum demand and so produces the line 63, and the control 52 produces the line 62. However, because the line 62 has a slope, the controls 52, 54 now requires a speed term.

The systems described are for use with a diesel engine in which the transducer senses control rod position and where the engine drives a road vehicle, the vehicle battery provides the required power for the system. However, it will be understood that there are other applications. For instance the guide vanes in the power turbine of an automotive gas turbine may be controlled. In this case the transducer 25 senses some particular engine parameter in accordance with which it is desired to control the guide vanes. This parameter may be related to the position of the guide vanes.

It will be apparent that although the switching device 27 acts additionally to rectify the a.c. signal, it need not do so, and if desired a separate rectifier could be employed.

We claim:

1. A control system for an engine comprising in combination an actuator for controlling the setting of a part associated with the engine, a control circuit coupled to the actuator to determine the position of said part, an oscillator, means deriving from said oscillator an a.c. signal having an amplitude dependent on the value of a system parameter, a switching device by way of which said a.c. signal is fed to a capacitor, the voltage across the capacitor providing an input to the control circuit, and means operable in synchronism with the oscillator for turning the switching device on at periods during the operation of the oscillator when said a.c. signal has stabilised.

2. A system as claimed in claim 1 in which the a.c. signal is fed to the switching device and capacitor by way of a cable.

3. A control system for an engine, comprising in combination an actuator for controlling the setting of a part associated with the engine, a control circuit coupled to the actuator to determine the position of said part, a transformer having a primary winding and a secondary winding, the primary winding being coupled to an oscillator and the secondary winding being connected through a cable and a switching device to a capacitor, means responsive to a system parameter for varying the coupling between the primary and secondary windings of the transformer and means operable in synchronism with the oscillator for turning the switching device on at periods during the operation of the oscillator when the voltage across the secondary winding has stabilised, whereby the voltage across the capacitor is indicative of the setting of the means for varying the coupling, the voltage across the capacitor providing an input to the control circuit.

4. A fuel supply system for an engine, comprising in combination a pump for supplying fuel to the engine, pump control means for determining the output of the pump, a first transducer for producing a first electrical signal representing pump output, a second transducer for producing a second electrical signal representing demand, means for producing a third electrical signal representing engine speed, a control circuit to which the first, second and third electrical signals are applied, the control circuit operating the pump control means to give the required pump output, at least one of said transducers comprising a transformer having its primary winding connected to an oscillator, and arranged so that the coupling between the primary and secondary windings is determined by the value of the parameter sensed by the transducer, whereby the amplitude of the a.c. signal in the secondary winding of the transformer is determined by the value of said parameter, a capacitor, a switching device, a cable coupling the secondary winding by way of the switching device to the capacitor, and means operable in synchronism with the oscillator for turning the switching device on at periods during the operation of the oscillator when the voltage across the secondary winding has stabilised, whereby the voltage across the capacitor is indicative of the value of said parameter, the voltage across the capacitor providing an input to the control circuit.

5. A system as claimed in claim 4 in which the control circuit includes a first summing amplifier which receives the first, second and third electrical signals and controls the pump control means, and a second summing amplifier which receives the first electrical signal and a reference and overrides the first amplifier to limit the pump output.

6. A system as claimed in claim 4 in which the control circuit includes a first summing amplifier which receives the first and second electrical signals and controls the pump control means, and a second summing amplifier which receives the third electrical signal and a reference and overrides the first amplifier to limit engine speed.

7. A system as claimed in claim 1 in which the switching device forms the sole means of rectifying the signal applied to the capacitor.

8. A system as claimed in claim 1 in which the means operable in synchronism with the oscillator comprises a first monostable circuit which is triggered by the oscillator and remains in its triggered state for a first predetermined period, and a second monostable circuit which is triggered by the first monostable circuit at the end of said first period, and remains in its triggered state for a second predetermined period, the switching device being driven on by the second monostable circuit while the second monostable circuit is triggered.

9. A system as claimed in claim 1 in which the switching device is a transistor.

10. A system as claimed in claim 9 in which the transister is a field effect transistor.

11. A system as claimed in claim 1 in which said means for deriving an a.c. signal comprises a pair of capacitors connected in series across the oscillator, one capacitor having a value determined by said system parameter and the other capacitor being connected to the switching device.

12. A system as claimed in claim 1 in which the oscillator is a square wave oscillator. 

1. A control system for an engine comprising in combination an actuator for controlling the setting of a part associated with the engine, a control circuit coupled to the actuator to determine the position of said part, an oscillator, means deriving from said oscillator an a.c. signal having an amplitude dependent on the value of a system parameter, a switching device by way of which said a.c. signal is fed to a capacitor, the voltage across the capacitor providing an input to the control circuit, and means operable in synchronism with the oscillator for turning the switching device on at periods during the operation of the oscillator when said a.c. signal has stabilised.
 2. A system as claimed in claim 1 in which the a.c. signal is fed to the switching device and capacitor by way of a cable.
 3. A control system for an engine, comprising in combination an actuator for controlling the setting of a part associated with the engine, a control circuit coupled to the actuator to determine the position of said part, a transformer having a primary winding and a secondary winding, the primary winding being coupled to an oscillator and the secondary winding being connected through a cable and a switching device to a capacitor, means responsive to a system parameter for varying the coupling between the primary and secondary windings of the transformer and means operable in synchronism with the oscillator for turning the switching device on at periods during the operation of the oscillator when the voltage across the secondary winding has stabilised, whereby the voltage across the capacitor is indicative of the setting of the means for varying the coupling, the voltage across the capacitor providing an input to the control circuit.
 4. A fuel supply system for an engine, comprising in combination a pump for supplying fuel to the engine, pump control means for determining the output of the pump, a first transducer for producing a first electrical signal representing pump output, a second transducer for producing a second electrical signal representing demand, means for producing a third electrical signal representing engine speed, a control circuit to which the first, second and third electrical signals are applied, the control circuit operating the pump control means to give the required pump output, at least one of said transducers comprising a transformer having its primary winding connected to an oscillator, and arranged so that the coupling between the primary and secondary windings is determined by the value of the parameter sensed by the transducer, whereby the amplitude of the a.c. signal in the secondary winding of the transformer is determined by the value of said parameter, a capacitor, a switching device, a cable coupling the secondary winding by way of the switching device to the capacitor, and means operable in synchronism with the oscillator for turning the switching device on at periods during the operation of the oscillator when the voltage across the secondary winding has stabilised, whereby the voltage across the capacitor is indicative of the value of said parameter, the voltage across the capacitor providing an input to the control circuit.
 5. A system as claimed in claim 4 in which the control circuit includes a first summing amplifier which receives the first, second and third electrical signals and controls the pump control means, and a second summing amplifier which receives the first electrical signal and a reference and overrides the first amplifier to limit the pump output.
 6. A system as claimed in claim 4 in whIch the control circuit includes a first summing amplifier which receives the first and second electrical signals and controls the pump control means, and a second summing amplifier which receives the third electrical signal and a reference and overrides the first amplifier to limit engine speed.
 7. A system as claimed in claim 1 in which the switching device forms the sole means of rectifying the signal applied to the capacitor.
 8. A system as claimed in claim 1 in which the means operable in synchronism with the oscillator comprises a first monostable circuit which is triggered by the oscillator and remains in its triggered state for a first predetermined period, and a second monostable circuit which is triggered by the first monostable circuit at the end of said first period, and remains in its triggered state for a second predetermined period, the switching device being driven on by the second monostable circuit while the second monostable circuit is triggered.
 9. A system as claimed in claim 1 in which the switching device is a transistor.
 10. A system as claimed in claim 9 in which the transistor is a field effect transistor.
 11. A system as claimed in claim 1 in which said means for deriving an a.c. signal comprises a pair of capacitors connected in series across the oscillator, one capacitor having a value determined by said system parameter and the other capacitor being connected to the switching device.
 12. A system as claimed in claim 1 in which the oscillator is a square wave oscillator. 